The effects of pulse electromagnetic field (PEMF) therapy in osteonecrosis will be evaluated in a randomized, double-blind study. Twenty patients with symptomatic osteonecrosis of either (or both) the femoral head or femoral condyle will be studied. Patients will be provided with molded casts containing electromagnetic coils and randomized to receive either PEMF (treatment group) or no PEMF (control group) across the site of involvement. The external casts with or without PEMF will be apalied to the involved area for 10 hours daily for a total of six months. Patients will be evaluated at 3 and 6 months by questionnaire, joint examination, bone scintigraphy and X-rays for evidence of healing of the osteonecrosis.